i) Field of the Invention
The present invention relates to a combined working machine for machining various types of cut on a workpiece held by a chuck of a headstock by bringing a tool of a tool post into contact with a workpiece at an appropriate position.
ii) Description of the Prior Arts
Conventionally, machine tools such as a lathe, a drilling machine or the like are special purpose machines for carrying out cutting, drilling or the like by a tool of a tool post into contact with a workpiece held by a chuck of a headstock, at a certain angle.
Further, a two spindle lathe having two headstocks arranged in parallel as a lathe for effectively performing cutting has been developed, as disclosed in Japanese Utility Model Publications No. Hei 1-31361 and No. Sho 59-40961. In the former case, as shown in FIG. 1, a bed 101 is formed with a slide surface 101a extending between both the ends of the bed 101. On this slide surface 101a, two headstocks 102A and 102B are installed in the central part and two saddles 104A and 104B having respective turret tool posts 103A and 103B are movably and locatably mounted on both the sides of the turret tool posts 103A and 103B. In this lathe, different cutting operations or the same cutting operation can be executed at the same time to reduce the machining time.
In the latter case, as shown in FIGS. 2 and 3, a carriage 105 or 106 is movably and locatably mounted so as to move toward two workpieces, WA and WB held by two spindle chucks and to be movable in the direction of the workpiece rotation. On the carriage 105, two turret tool posts 107A and 107B are mounted, and on the carriage 106, two tool posts 108A and 108B are mounted. Hence, by moving the carriage 105 or 106, the turret tool posts 107A and 107B or the two tool posts 108A and 108B are simultaneously moved to perform the cutting of the two workpieces WA and WB at the same time.
Further, another conventional two spindle lathe has been proposed, as disclosed in Japanese Patent Publication No. Sho 61-3601. In this case, as shown in FIG. 4, a third turret tool post 110 capable of corresponding to both main spindles 109A and 109B is provided between first and second turret tool posts 111 and 112 directing to the main spindles 109A and 109B. By providing the third turret tool post 110, two kinds of machining can be applied to one workpiece at the same time. For example, by using two tools which are attached to the turret tool posts 110 and 111 and are set to different depths of cutting loads, two cutting operation with different chip loads, which are usually machined by two steps, can be carried out on the workpiece held by a chuck of the main spindle 109A at the same time.
However, the conventional machine tool is a machine for exclusive cutting by using a fixed tool or for drilling by using a rotary tool such as a drill. Also, in the conventional lathe, in addition to cutting, drilling along a rotational axis of a workpiece can be performed, but offset drilling for drilling a bore in an offset position from the rotational axis of the workpiece can not be machined. Thus, when a combined machining operation such as cutting and offset drilling is required on one workpiece, after the workpiece is machined according to the first operation by a first machine tool, the workpiece is detached from the chuck of the first machine tool and is chucked to a second machine tool to be machined according to the second operation. Hence, in this case, combined working can not be effectively machined.
In the conventional lathe, although two turret tool posts each include a two-dimensional moving mechanism, it is conceivable to add another moving mechanism in the vertical direction so as to move the turret tool post in the three-dimensional space when the combined machining is executed. However, in this case, when the offset drilling is performed, the drilling direction is only the horizontal direction. Therefore, the turret tool post must be moved from the vertical direction to the horizontal position for carrying out the offset drilling. That is, the vertical travel distance of the turret tool post becomes long and the height of the machine tool becomes tall so that the stability of the machine tool deteriorates.